T cell invasion of the stem cell compartment during immune-mediated GI damage

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Despite the importance of intestinal stem cells (ISCs) for epithelial maintenance in the gastrointestinal (GI) tract and the clinical significance of inflammatory intestinal disorders and immune-mediated GI damage, the potential of the immune system to directly engage with the ISC compartment remains poorly understood. GI graft vs. host disease (GVHD) is one of the greatest challenges for allogeneic hematopoietic/bone marrow transplantation (allo-BMT), causing severe toxicity, necessitating deeply immunosuppressive interventions, and limiting the wider usage of allo-BMT for potentially curable conditions. We have found that acute GVHD leads to substantial reduction of Lgr5+ ISCs and the Paneth cells providing their epithelial niche. While there is limited understanding of the precise mechanisms by which immune responses induce ISC compartment damage and regeneration, it is not possible to fully understand BMT-related complications in the GI tract or how immune cells may impact specific epithelial components without examining the three-dimensional (3-D) tissue environment of the intestines and the proximity of immune responses to the ISC compartment. We seek to understand the fundamental interactions occurring between the immune system and the ISC compartment, how these interactions are engaged in the context of hematopoietic transplantation, and how the underlying biology may be manipulated therapeutically for clinical intervention. To address these goals, we have developed a research proposal emphasizing 3-D imaging of immune effectors within GI tract, mechanistic ex vivo modeling of murine and human immune cell recruitment to the ISC compartment, and in vivo validation in experimental transplant models. We have also assembled a multi-disciplinary team of collaborators at the forefront of basic and translational immunology, ISC biology, and advanced microscopic imaging. Our preliminary findings indicate that the ISC compartment is the first site of allogeneic T cell invasion within the intestinal mucosa after BMT and thus the initial target of GVHD. Furthermore, we have found that co-cultures of immune cells and intestinal organoids can be used to model and mechanistically dissect these processes. Using 3-D confocal and 2-photon intravital imaging, we have developed the capacity to accurately quantify loss of ISCs, specific invasion of the ISC compartment, and localization of T cell homing ligands during homeostasis and during active immunity. We have also developed strategies for analysis of in vivo lineage- specific gene expression within the ISC compartment. This study will thus test the hypothesis that lymphocyte recruitment to and regulation of the ISC compartment are central features of GI damage post-transplant, impacting both physiologic and pathologic mucosal responses, and we will evaluate approaches to modulate lymphocyte homing and promote recovery of injured epithelium. This project will lead to a mechanistic understanding of fundamental interactions between the ISC compartment and the immune system, opening a new direction for treatment of GVHD and other GI disorders by protecting ISCs and augmenting regeneration.